Two part metal packages, commonly referred to as cans, are widely used in the semiconductor industry to contain discrete devices such as transistors. Such packages typically comprise a header upon which a semiconductor device, or die, is bonded and a cap which covers the device on the header and is welded to the header to create a hermetically sealed environment for the device.
When packaging semiconductor devices in metal cans, one must place the cap over the appropriate location on the header after the die bond and wire bond processes are complete. Next, the assembled, but unwelded package must be moved to a welding machine to finish the packaging operation. In many instances, these operations must take place in a controlled environment, such as a glove box, to ensure that the atmosphere sealed into the package is non-destructive.
In order that the unit cost of the headers and caps be reasonable, the dimensional control in their manufacture is somewhat relaxed. Thus, the fit between any particular header and any particular cap is likely to be somewhat sloppy until the weld is accomplished. This presents the problem that the assembled, but unwelded package may come apart during the handling necessary between the assembly and welding operations. This is particularly likely and troublesome when these operations are performed by hand in a glove box. In that case, the operator's dexterity is somewhat limited and the efficiency of the operation is very quickly reduced by significant separation of headers and caps.
Previously, the mechanical integrity of the assembled, but unwelded parts was improved by means of a slight deformation of the caps prior to assembly. This was accomplished by feeding the caps between a pair of spinning wheels which were spaced so as to slightly crimp the caps. This method did improve the mechanical integrity of the unwelded packages. However, it was found that an amount of crimping comparable to the tolerance in the caps as delivered by the vendor is need to adequately hold the caps on the headers. As will be apparent to one skilled in the art, it is extremely difficult to reliably apply a deformation in an amount comparable to the tolerance of that dimension of a part. This results in some parts which are overcrimped and will not properly seat on a header and in some parts which are undercrimped and will not stay on the header.